This invention relates to silicon-on-insulator substrates and more particularly to forming a high quality buried oxide layer by heating a semiconductor substrate, implanting oxygen into the substrate in several incremental steps and annealing the substrate.
In order to reduce capacitance and to electrically isolate devices, silicon-on-insulator (SOI) wafers are used in place of bulk Si wafers. One approach to forming an SOI wafer is to use separation by implantation of oxygen (SIMOX) where a buried oxide layer is formed in a wafer by implanting oxygen ions and then annealing at high temperatures.
An example of an advance SIMOX process is described in U.S. Pat. No. 5,930,643 which issued on Jul. 27, 1999 to D. K. Sadana and J. de Souza entitled xe2x80x9cDefect Induced Buried Oxidexe2x80x9d which describes implanting oxygen into a Si wafer at high temperature to form a stable defect region in the Si followed by implanting oxygen at a temperature below 300xc2x0 C. to form an amorphous Si region adjacent the stable defect region.
U.S. Pat. No. 6,043,166 which issued Mar. 28, 2000 describes forming a high quality buried oxide (BOX) layer with extremely low doses of oxygen followed by two high temperature oxidation anneals to eliminate defects in the silicon above the buried oxide by forming silicon dioxide as part of the buried oxide in the region where the defects were present.
U.S. Pat. No. 6,090,689 which issued Jul. 18, 2000 describes forming Silicon-on-Insulator substrates incorporating the steps of ion implanting oxygen into a silicon substrate at an elevated temperature, ion implanting oxygen at a temperature below 100 degrees xc2x0 C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone from the amorphous silicon layer and then silicon oxide to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The low temperature implant results in the formation of a buried amorphous layer at the location where the oxide is to be formed. The amorphous silicon layer contains both dissolved and precipitated oxygen which forms polycrystalline silicon to provide sites for nucleating oxide growth and paths for rapid diffusion of oxygen along the polycrystalline grain boundaries.
In accordance with the present invention, a method for forming a semiconductor-on-insulator (SOI) substrate having a high quality buried oxide layer is described comprising the steps of selecting a semiconductor substrate containing silicon and having a major surface, heating the semiconductor substrate to a first temperature in the range from 100 to 800xc2x0 C., first implanting oxygen into the major surface at a first energy to deposit oxygen in a range centered about a first depth whereby a buried damaged region is formed, heating/cooling the semiconductor substrate to a second temperature below 300xc2x0 C., second implanting oxygen into the major surface at a second energy to deposit oxygen in a range centered about a second depth whereby a buried amorphous region of semiconductor material is formed, heating/cooling the semiconductor substrate to a third temperature in the range from 100 to 800xc2x0 C., third implanting oxygen into the major surface at a third energy to deposit oxygen in a range centered about a third depth whereby an additional buried damaged region is formed, and annealing the semiconductor substrate above 1100xc2x0 C. for a first time period to form the high quality buried oxide layer.
The invention further includes the step of cleaning the substrate to remove debris and particulates prior to performing one or more of the steps of first, second, and third implanting.
The invention further includes the step of forming a patterned mask on the substrate prior to performing one or more of the steps of first, second, and third implanting and of removing the patterned mask prior to annealing.
The invention further includes the step of implanting in place of oxygen or with oxygen the elements: nitrogen, carbon, neon, helium, argon, krypton, xenon, fluorine, radon, silicon, aluminum, boron, phosphorus, titanium, chromium, iron, other elements from the Periodic Table or combinations thereof.